Optical networks and the like are deploying control plane systems and methods that span multiple layers (e.g., wavelength division multiplexing (WDM), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), Optical Transport Network (OTN), Ethernet, and the like). Control plane systems and methods provide automatic allocation of network resources in an end-to-end manner. Exemplary control planes may include Automatically Switched Optical Network (ASON) as defined in G.8080/Y.1304, Architecture for the automatically switched optical network (ASON) (February 2005), the contents of which are herein incorporated by reference; Generalized Multi-Protocol Label Switching (GMPLS) Architecture as defined in Request for Comments (RFC): 3945 (October 2004) and the like, the contents of which are herein incorporated by reference; Optical Signaling and Routing Protocol (OSRP) from Ciena Corporation which is an optical signaling and routing protocol similar to PNNI (Private Network-to-Network Interface) and MPLS; or any other type control plane for controlling network elements at multiple layers, and establishing connections there between. Control plane systems and methods use bandwidth advertisements to notify peer nodes of available link capacity. The bandwidth advertisements exchange information over a dedicated and well known communication channel with peers on opposite ends of the communication link.
The aforementioned control planes are each source-based routing control planes meaning connections, e.g. subnetwork connections (SNCs), are routed by the source nodes. Disadvantageously with source-based routing control planes, there is no control on the sequence of restoring connections after faults even if higher bandwidth connections are released first from the point of failure. This leads to three broad categories of problems, namely network fragmentation, crank-backs for tail-end connections, and inability to prioritize higher bandwidth connections over lower bandwidth connections. With respect to network fragmentation, conventionally, there can be cases where smaller SNCs, e.g. STS3c/STS12c/ODU0/ODU1, reroute/restore first so as to “fragment” the network such that larger SNCs, e.g. STS24c/STS48c/ODU2/ODU3, will fail to restore. This is because of two reasons—a) smaller connections fragment the network making it no longer possible for larger connections even though a cumulative bandwidth in the network is available for the larger connections (i.e., the cumulative bandwidth is non-contiguous in the network), and b) total available bandwidth is just enough to accommodate a larger bandwidth connection. With respect to b), if the smaller bandwidth connection is established first, then larger bandwidth connection will never come up, and remaining bandwidth will go waste until there is a reconfiguration in the network.
Crank-backs generally are when blocking occurs, a signaling setup request “cranks-back” to a source node to try and alternative path which of course increases total restoration time. Conventionally, there can be a situation where larger connections, e.g., STS48c/12c SNCs re-route/restore first reserving network bandwidth such that tail End n3xSTS3c/STS1 SNCs will fail to restore, and crank-back and then retry. This can happen since routing updates are much slower than signaling and the same link can be given to multiple connections (overbooked) in an event of mesh restoration. Finally, higher bandwidth connections cannot be prioritized over lower bandwidth connections with conventional systems and methods as there is no control on the sequence of restoring connections in a source routing control plane. Further, there are no mechanisms in the aforementioned control planes for considering shared risk groups for computing protect paths. A shared risk link group (SRLG) is a set of two or more links, for which a failure of any one link in the SRLG is associated with a relatively high risk of failure of the other links in the SRLG. For example, two SNCs traversing a same physical link would be in an SRLG meaning a fault on the same physical link would affect both the SNCs. Two paths are SRLG-disjoint if no two links in the two paths are members of any one SRLG.